Transfer roller

ABSTRACT

Apparatus for the electrostatic transfer of a developed latent image from a master to a conductive receiving surface is provided and utilizes a transfer roller that traverses the carrier web to bring the master that is attached to the web adjacent to, but not in contact with, the conductive receiving surface.

BACKGROUND OF THE INVENTION

This invention relates generally to apparatus for the electrostatictransfer of a developed image from a master to a receiving surface. Morespecifically, it pertains to the movable transfer means that contactsand traverses a carrier means which supports the master to effect theelectrostatic transfer.

The permanent master and the transfer means are used repeatedly toproduce high resolution and high quality images on receiving surfaces,such as printed circuit boards. Receiving surfaces, such as printedcircuit boards, have traditionally been produced by individuallaminating, exposing, developing, etching and stripping processes wheredry film photoresist has been used to produce the conductive wiringpatterns. Heretofore, there has been no method or apparatus available toproduce a plurality of copies of conductive wiring patterns from asingle master copy of the desired wiring pattern utilizing a dry filmresist and photoimaging. There are many factors which prevented thistype of a system from being employed to manufacture multiple copies froma single master.

Where liquid toner was employed, it was extremely difficult to attemptto clean excess toner or prevent the buildup of excess toner from themaster. The ability to obtain a uniform and full width image over alarge area, such as a 24 inch by 24 inch surface, was severelyrestricted. Trapped air or liquid solvent can frequently cause voids inthe electrostatically transferred developed image. Where electrostaticswere used to effect the transfer, the ability to separate the mastersurface and the receiving surface was critical and extremely difficultbecause of the electrostatic forces involved. Lastly, the availabilityof reliable and durable equipment to effect repeated transfers of thedeveloped image on a master to a receiving surface was severely limited.

These problems are solved in the design of the apparatus of the presentinvention by providing transfer means that contacts the carrier of themaster to effect an electrostatic transfer of a developed image to areceiving substrate by traversing the carrier means for a distance equalto at least the length of the master.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide transfer rollermeans that are cooperative with the carrier means to move the masterwith the developed latent image adjacent to the conductive receivingsurface to effect the electrostatic transfer of the developed image.

It is another object of the present invention to provide transfer meansto maintain the predetermined angular ranges for the leading andtrailing angles of the carrier means with respect to the conductivereceiving surface to ensure discrete point of contact transfer of thedeveloped image on the master to the conductive receiving surface.

It is a feature of the present invention that the transfer roller meanstraverse over the carrier web means to which the master is attached toposition the master adjacent to the conductive receiving substrate toelectrostatically transfer the developed image on the master across thefinite liquid-filled gap to the receiving substrate.

It is another feature of the present invention that the angle of thecarrier web means and the attached master is controlled with respect tothe conductive receiving substrate to obtain the full width and highquality electrostatically transfer image on the conductive receivingsurface.

It is yet another feature of the present invention that the carrier webmeans is kept uniformly tensioned as the transfer roller means traversesthe carrier web means to achieve the high quality and high resolutionimage transfer to the conductive receiving surface.

It is an advantage of the present invention that discrete point transferof the developed image to the conductive receiving surface occurs.

It is another advantage of the present invention that entrapped air andexcessive insulating solvent liquid is avoided between the carrier webmeans and the conductive receiving surface so that incomplete transferof the image and creation of a standing wave of entrapped material isavoided.

It is yet another advantage of the present invention that there is norippling of the carrier web means.

It is still another advantage of the present invention that the carrierweb means with the master attached and the conductive receiving surfaceare separate and are in close proximity only at the discrete points oftransfer in the transfer window to avoid excessive electrostatic forcethat could pull the master and the conductive receiving surface intocontact.

It is still another advantage of the present invention that the leadingangle of the carrier web means with respect to the conductive receivingsurface is large enough to prevent the electrostatic force on theconductive receiving surface from pulling the master and the conductivereceiving surface into contact and to open up the carrier web means, andstill small enough to provide a good transfer window and not tooverstress the carrier web means and the mechanics of the apparatus topermit repeated transfers to be accomplished.

These and other objects, features and advantages are obtained by use ofa master attached to a carrier web means which tranfers a developedimage to a conductive receiving surface via the use of transfer rollermeans contactable with the carrier web means to move the master adjacentto but not into contact with the conductive receiving surface to effectthe electrostatic transfer of the developed image by having the transferroller means traverse a distance at least equal to the length of themaster. The carrier web means is retained by tensioning roller meanswhich are positioned so the transfer roller means is intermediate thetensioning roller means and the retention roller means to thereby causethe carrier web means to form a leading angle and a trailing angle withthe conductive receiving surface as the transfer roller means traversesthe carrier web means during the electrostatic transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention willbecome apparent upon consideration of the following detailed disclosureof the invention, especially when it is taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a side elevational view of the apparatus for transferring theelectrostatically developed image from a master to a conductivereceiving surface;

FIG. 2 is an enlarged side elevational view of the transfer roller meansapparatus utilized to transfer the developed latent image from themaster attached to the carrier web means to the conductive receivingsurface; and

FIG. 3 is a sequential diagrammatic illustration of the transfer rollermeans as it traverses the carrier web means and the attached master toposition the developed master adjacent to, but not in contact with, theconductive receiving surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a side elevational diagrammatic illustration of theelectrostatic imaging apparatus, indicated generally by the numeral 10.Apparatus 10 has a support frame 11 to which are mounted toner tankassembly 12, cleaning station tank and feed line assembly 13, non-polarinsulating solvent tank assembly 14, and vacuum pump assembly 15. Eachof the tank assemblies 12, 13 and 14 have appropriate hoses and pumps toeither distribute the toner to the toning station 25 or the non-polarinsulating solvent to the master cleaning station 27 and wicking station21, respectively.

The permanent master is a multiple layered structure having a base layerof a suitable flexible and non-conductive plastic, such as apolyethylene terephthalate sold under the tradename Mylar®, which iscoated with an aluminum layer and a layer of photosensitive material,such as dry film or liquid photoresist. The permanent master is producedby exposing the desired pattern, such as through a mask, to actinicradiation. The exposed pattern on the electrostatically imageablesurface of the master, once thus cross-linked, creates a persistentlatent image. This latent image will hold an electrostatic charge whenexposed to a charging apparatus, such as corona 31. The charged imageattracts the toner particles of an appropriate toner when the master 40with the image thereon is passed through toning station 25.

The master, seen as 40 in FIG. 2, is placed on a stationary platen 16 ofFIG. 1. Alignment pins 18 assure that the master 40 is properlypositioned on the stationary platen 16 via the use of pin cams 19 andplaten cams 20, or other appropriate apparatus. The master 40 is thenpicked up by the carrier web means 36 by having the transfer assembly,indicated generally by the numeral 33, move over the platen 16 bytraversing the master transport rod 39 (see briefly FIG. 1). Thetransfer assembly 33 is aligned and registered to the master 40 andplaten 16 by the engagement of pins 38 on the transfer assembly 33 withthe pin receptacles 17.

An electrical charge is supplied to the carrier web means 36, which isformed from a flexible, non-conductive material having a conductivecoating. Silver coated Mylar® plastic has been successfully employed.The electrical charge is carried by the conductive coating and createsthe electrostatic force which holds the master on the carrier web means36. The transfer assembly 33 then returns to the start position shown inFIG. 1, carrying the master 40 with it.

A conductive receiving surface 41, such as a copper circuit board, whichis preferably two-sided and is diagrammatically illustrated in FIG. 3,is placed on the platen 16 of FIG. 1 and is registered so it will beprecisely aligned with the master 40 by the alignment pins 18 that arepositioned by means of cams 19, or other appropriate apparatus. Theposition of the platen 16 can be controlled by any appropriateapparatus, such as cams 20, if necessary.

The transfer assembly 33, once the conductive receiving surface 41 isproperly positioned on platen 16, carries the carrier web means 36 andthe master 40 of FIGS. 2 and 3 toward the platen 16. The master 40passes over the charging corona 31 of FIG. 1, which charges thepersistent latent image on the master 40 and then passes over the toningstation 25, which includes reversing roller 26 and development tonerelectrode 28, to develop the latent image. Excess solvent is removedfrom the area around the developed image by the reversing roller 26 inconjunction with the depressant corona 24, which removes the excessivenon-polar insulating solvent from around the developed image beforetransfer. A web wiper 29, also shown in FIG. 1, is used to clean themaster 40 as part of the cleaning station 27 after image transfer hasoccurred.

Wicking station 21 then applies a layer of liquid containing non-polarinsulating solvent to the conductive receiving surface 41 of FIG. 3. Gapspacing and charging strips 22, preferably about 5 mils thick and formedof Mylar® plastic coated with aluminum on the bottom surface, are placedalong opposing sides of the conductive receiving surface 41 bydispensing apparatus (not shown) in the wicking station 21 as thetransfer assembly 33 passes over the surface 41 (not shown) on theplaten 16.

The transfer assembly 33 stops when the master 40 on the carrier webmeans 36 is positioned precisely over the conductive receiving surface41 on the platen 16, so that the master 40 and the conductive receivingsurface are coincident.

As best seen in the diagrammatic illustration in FIG. 3, the transferassembly 33 has electrically grounded web tensioning roller means 35mounted on an idler arm 42 that is movable by means of the spring 44 tocause the roller means 35 to turn about a suitable support, such as abearing (not shown), to maintain the proper tension on the carrier webmeans 36. Once properly positioned, the transfer roller means 34contacts the back or upper side of the carrier web means 36 andtraverses a distance equal to at least the length of the master 40 tobring the master adjacent to, but not in contact with, the conductivereceiving surface 41 at discrete points along the entire length of themaster. Web retention roller means 32 applies the high voltage charge,varying from about 200 to about 3,000 volts dependent upon the master,to the silver surface of the carrier web means 36 to pick up and retainthe master 40 on the carrier web means 36. Web retention roller means 32combines with the tensioning roller means 35 and the transfer rollermeans 34 to permit the transfer roller means 34 to smooth out thecarrier web means 36 and the master 40 to obtain a smooth, continuoussurface that is free of ripples.

As is best seen in FIG. 3, the transfer roller means 34 establishes withthe carrier web means 36 a leading angle 45 and trailing angle 46. Theseleading and trailing angles 45 and 46 vary as the transfer rollertraverses the entire length of the master 40. The leading angle 45 andthe trailing angle 46 will vary in angulation depending upon thediameter of the transfer roller, the speed of travel of the transferroller across the carrier web means 36, the length of the master 40, thesize of the transfer gap between the master 40 and the conductivereceiving surface 41, and the type of toner used. The leading angle 45can vary from between about 1° to about 10° from the front at thebeginning of contact with the master 40 to about 6° to about 30° at theend of the master 40. Similarly, the trailing angle 46 can vary frombetween about 45° down to about 221/2° at the beginning of contact withthe master 40 to about 221/2° to about 10° at the end of the master 40.For example, with a 11/2 inch diameter transfer roller, a 24 inch longmaster, a transfer roller traversing speed of about 10 inches per secondand about a 5 mil thick transfer gap, the leading angle 45 was about 1°at the beginning of contact with the master 40 and about 6° at the endof the master 40. The trailing angle 46 at these two locations variedbetween about 221/2° to about 12°. As a general guide, it is notdesireable to use a larger than necessary angle for the leading andtrailing angles 45 and 46.

The transfer roller means 34, with the web tensioning roller means 35and the web retention roller means 32, maintain a uniform tension on thecarrier web means 36 to ensure discrete point to point transfer of thedeveloped image on the master to the conductive receiving surfacethrough the transfer window 37 in FIG. 3 and to avoid entrapping air andexcessive non-polar insulating liquid solvent between the two surfaces.The transfer window 37 is that area on the master 40 which the diameterof the transfer roller brings into transfer proximity for discrete pointtransfer with the conductive receiving surface 41.

The finite gap between the two surfaces is filled with the non-polarinsulating solvent across which the toner particles travel as describedin copending application Ser. No. 883,797 filed July 9, 1986 andassigned to the assignee of the present invention, herein specificallyincorporated by reference in pertinent part.

The electrostatic field between the master 40 and the conductivereceiving surface 41 is established by the application of a charge onthe conductive receiving surface 41. This charge is supplied by anindependent high voltage source (not shown) through the aluminum coatingon the gap spacing and charging strips 22. This electrostatic fieldpermits the transfer of the developed image on the master 40 to theconductive receiving surface 41.

The transfer roller means 34 of FIG. 2 traverses the entire length ofthe master 40 by being driven along support shaft 48 by the drive motor49, turning master screw drive 39 that moves transport roller drive nut55. Once the transfer roller means 34 has traversed this entire lengthas is illustratively shown in FIG. 3, its guide roller 50 rides up theramp plate 51, connected to web backing plate 61, into the retentiongroove 52 as the stop block 57 engages the stop bracket 62. Thispositioning of the guide roller 50 continues until the entire transferassembly 33 is moved back to the start position seen in FIG. 1. Theriding of the guide roller 50 up the ramp plate 51 causes the pivot arm59, connected to bearing 54, to pivot about pin 60 to raise the transferroller means 34 up and allow the carrier web means 36 to be flat againstthe web backing plate 61. The drive motor 49 then returns the transferroller means 34 and the web backing plate 61 to the start position. Bytraversing support shaft 48 until bearing 54 abuts stop plate 58 theguide roller 50 is raised out of the retention groove 52 to separate thetransfer roller means 34 from the ramp plate 51 and the web backingplate 61 to which ramp plate 51 is attached. The disengagement of thetransfer roller means 34 from the retention groove 52 allows the webbacking plate 61 to be driven against stop bracket 62. This isaccomplished by actuating a retractable stop pin 63, mounted to thesupport frame 11 (not shown), in front of stop block 57 as the transferassembly 33 is driven towards the platen 16 of FIG. 1 by the main drivescrew shaft 64. After the web backing plate 61 abuts stop bracket 62,the retractable stop pin 63 is retracted to a raised position. The webbacking plate 61 is now in the transfer position. The transfer rollermeans 34 is then in position to again traverse the carrier web means 36to effect the electrostatic transfer from the master 40 to theconductive receiving surface 41.

The use of the terms persistent and permanent latent image with respectto the master 40 is intended to connote that the image is durable,lasting over a long period of time, as well as not changing in the highquality and resolution of its transferred image. For example, thepersistent latent image can last months and, perhaps, years once exposedinto the electrostatically imageable surface of the master 40, underproper storage conditions. Additionally, as many as 5,000 images havebeen transferred from a single master.

While the preferred structure in which the principles of the presentinvention have been incorporated is shown and described above, it is tobe understood that the invention is not to be limited to the particulardetails thus presented but, in fact, widely different means may beemployed in the practice of the broader aspects of this invention. Forexample, the master or the electrostatically developable surface canalso include zinc oxide, cadmium sulfide, selenium or suitable organicphotoconductors. The scope of the appended claims is intended toencompass al obvious changes in the details, materials and arrangementsof parts that will occur to one of ordinary skill in the art upon areading of this disclosure.

What is claimed is:
 1. Apparatus for the electrostatic transfer of adeveloped image from an electrostatically developable surface to aconductive receiving surface, comprising in combination:(a) a supportframe; (b) supporting means for supporting the conductive receivingsurface connected to the support frame; (c) carrier means connected tothe frame for supporting the electrostatically developable surface; (d)positioning means connected to the frame for positioning the carriermeans relative to the supporting means to permit the electrostatictransfer to occur; (e) transfer means movably connected to the frame andcontactable with the carrier means to move the electrostaticallydevelopable surface adjacent to, but not in contact with the conductivereceiving surface to effect the electrostatic transfer of the developedimage, the transfer means being reversible and traversing the carriermeans a distance equal to at least the length of the electrostaticallydevelopable surface; (f) tensioning means for tensioning the carriermeans, the tensioning means being movably connected to the frame andcausing the carrier means to form a trailing angle with the conductivereceiving surface as the transfer means traverses the carrier meansduring the electrostatic transfer; and (g) retention means for retainingthe carrier means connected to the frame and positioned such that thetransfer means is intermediate the tensioning means and the retentionmeans causing the carrier means to form a leading angle with theconductive receiving surface as the transfer means traverses the carriermeans during the electrostatic transfer.
 2. The apparatus according toclaim 1 wherein the retention means is further electrically charged. 3.The apparatus according to claim 2 wherein the tensioning means iselectrically grounded.
 4. The apparatus according to claim 3 wherein thecarrier means further has a conductive surface adjacent the master. 5.The apparatus according to claim 4 wherein the carrier means further hasthe conductive surface connected to a non-conductive substrate.
 6. Theapparatus according to claim 5 wherein the non-conductive substratefurther is flexible.
 7. The apparatus according to claim 6 wherein thecarrier means is further a generally rectangular and longitudinallyextending web between the tensioning means and the retention means. 8.The apparatus according to claim 7 wherein the conductive surface of thecarrier means further comprises a coating of a silver-containingcompound.
 9. The apparatus according to claim 7 wherein theelectrostatically developable surface further comprises a multilayersheet having a first non-conductive layer adjacent the carrier means, anintermediate conductive layer and a third photosensitive material layercontaining a developable persistent latent image.
 10. The apparatusaccording to claim 5 wherein the leading angle increases as the transfermeans traverses from the tensioning means toward the retention means.11. The apparatus according to claim 10 wherein the leading angle variesbetween about 1° to about 30°.
 12. The apparatus according to claim 10wherein the trailing angle decreases as the transfer means traversesfrom the tensioning means to the retention means.
 13. The apparatusaccording to claim 11 wherein the trailing angle varies from about 10°to about 45°.
 14. The apparatus according to claim 5 wherein thetransfer means is a rotatable roller.
 15. The apparatus according toclaim 14 wherein the tensioning means is a spring loaded roller.
 16. Theapparatus according to claim 15 wherein the retention means is astationary roller.
 17. The apparatus according to claim 1 wherein theretention means is electrically grounded.
 18. The apparatus according toclaim 2 wherein the tensioning means is electrically charged.
 19. Theapparatus according to claim 6 wherein the flexible nonconductivesubstrate is polyethylene terephthalate.
 20. Apparatus for theelectrostatic transfer of a developed image from an electrostaticallydevelopable surface supported by carrier means to a conductive receivingsurface, the improvement comprising in combination:(a) transfer meanscontactable with the carrier means to move the electrostaticallydevelopable surface adjacent to, but not in contact with the conductivereceiving surface to effect the electrostatic transfer of the developedimage, the transfer means being reversible and traversing the carriermeans a distance equal to at least the length of the electrostaticallydevelopable surface; (b) tensioning means for tensioning the carriermeans causing the carrier means to form a trailing angle with theconductive receiving surface as the transfer means traverses the carriermeans during the electrostatic transfer; and (c) retention means forretaining the carrier means and positioned such that the transfer meansis intermediate the tensioning means and the retention means causing thecarrier means to form a leading angle with the conductive receivingsurface as the transfer means traverses the carrier means during theelectrostatic transfer.